fixed local user video window hide issue when multiple users join on same channel

[Nilupul96]

Pull request checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes/features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)
• The GitHub Actions pass building and linting. Linter returns no warnings or errors.
• The QA checklist below has been completed

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• [x ] Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

1. When multiple users join on the same channel if one remote user leaves the channel hide their local user window from the layout.
2. If Main Agora user mute their video and mute/unmute the audio then the MainAgora User window is disappeared.

Issue Number: N/A
https://github.com/AgoraIO-Community/VideoUIKit-Flutter/issues/182

What is the new behavior?

When a user leaves the channel do not hide their own user window from the layout.

Does this introduce a breaking change?

• Yes
• No

QA Checklist

VideoUIKit Update Checklist (Minor or Patch Release)

• Using the latest version of Agora's Video SDK
• Example apps are all functional
• Core features are still working (both ways across platforms)
  • Camera + Mic muting works for local and remote users
  • Users are added and removed correctly when they join and leave the channel
  • Older versions of the library gracefully handle changes (Create issue if not)
  • Builtin buttons all work as expected
• Any newly deprecated methods are flagged as such inline and in documentation